Security papers are used for manufacturing security documents such as banknotes, passports, postage stamps and the like. Conventionally, a wide variety of security features are incorporated into such security papers or provided on their surface. Known examples of such security features include watermarks, embedded and windowed security threads, fluorescent pigments and the like.
Watermarks, which are recognizable images or patterns in paper that appear as various shades of lightness/darkness when viewed by transmitted light or by reflected light atop a dark background, have provided protection against counterfeiting security documents for hundreds of years. In fact, watermarks and their engaging designs are the most readily recognized security feature available to the general public for the authentication of security documents such as banknotes.
There is, however, an ongoing need to improve the security or counterfeit resistance of watermarked security documents.
The present invention addresses this need by providing enhanced and thus more counterfeit-resistant watermarks in paper and paper-like materials. Specifically, the present invention provides a security sheet or document having one or more enhanced watermarks, the sheet or document comprising:                a fibrous sheet material including one or more watermarks, wherein each watermark has one or more first regions with reduced fiber densities relative to surrounding regions of the fibrous sheet material and one or more second regions with similar or increased fiber densities relative to surrounding regions of the sheet material, and wherein each watermark has an upper or face portion and a lower or back portion; and        means for enhancing the one or more watermarks by rendering them visually enhanced, machine detectable/readable, or both, said means selected from the group of:        a) one or more film-like or foil-like security elements at least partially covering the face or the back portion of the one or more watermarks, wherein the one or more film-like or foil-like security elements is in the form of a band, strip, stripe, thread, or patch;        b) one or more non-film-like, non-foil-like security elements contained on or within either or both the one or more first regions and the one or more second regions of the one or more watermarks, the one or more security elements selected from the group of:                    i. recognizable or discernible indicia; and            ii. one or more substances that are color-imparting and/or machine detectable or machine readable including, but not limited to, ultraviolet (UV) or infrared (IR) reactive, luminescent (i.e., fluorescent or phosphorescent), thermochromic, photochromic, electrochromic, metal, or magnetic security fibers, taggants, planchettes, dyes, pigments;                        c) one or more polymer or resinous materials contained within the one or more first regions and optionally the one or more second regions of the one or more watermarks, the one or more polymer or resinous materials having an index of refraction or combined (final) index of refraction substantially similar to that of cellulose;        d) an optionally windowed second paper layer covering either the face or the back portion of the one or more watermarks; and/or        e) one or more transparent or translucent areas surrounding each of the one or more watermarks.        
In a first exemplary embodiment, the inventive security sheet or document is a single- or multi-ply paper that comprises:                a first paper layer including one or more watermarks, each surface of the paper layer displaying either the upper or face portion of the watermark(s) or the lower or back portion thereof;        one or more film-like or foil-like security elements that at least partially cover the upper or face portion or the lower or back portion of the one or more watermarks; and optionally        a second paper layer having a reduced basis weight compared to the first paper layer and optionally one or more through windows, the second paper layer covering either the upper or face portion or the lower or back portion of the one or more watermarks.        
The film-like or foil-like security element preferably has a color different from the watermark(s) and the surrounding paper thereby enhancing the appearance of the underlying or overlying watermark(s) as well as enhancing the contrast between the underlying or overlying watermark(s) and the surrounding paper.
In one such embodiment, the film-like or foil-like security element(s) is a micro-optic security device that projects one or more synthetic images such as the MOTION™ micro-optic security device, which is described in, for example, U.S. Pat. No. 7,333,268. Such devices display colored images on a transparent or tinted background and thus are well suited for use in combination with underlying printed information. It has been observed that these security devices appear to provide the watermark(s) with a multi-tonal appearance. As will be readily appreciated by those skilled in the art, multi-tonal watermarks present an even greater challenge to a counterfeiter.
In a preferred embodiment, the micro-optic security device is in the form of a surface-applied patch that covers all or part (e.g., one-half) of a watermark, the watermark containing one or more polymer or resinous materials within the first and/or second regions of the watermark, the one or more polymer or resinous materials having an index of refraction or combined (final) index of refraction substantially similar to that of cellulose. In one such embodiment, the region(s) also contains one or more features selected from the group of increased fiber density areas in the form of recognizable or discernible indicia, one or more substances that are color-imparting, and one or more so-called second level security features that are machine detectable or machine readable (e.g., UV or IR reactive, luminescent, thermochromic, photochromic, electrochromic, metal, or magnetic security fibers, taggants, planchettes, dyes, pigments).
As will be readily appreciated by those skilled in the art, the micro-optic security device may also be in the form of a surface-applied elongate security band, strip, stripe, or thread, or a partially embedded elongate security band, strip, stripe, or thread that is present in window regions of a second paper layer (i.e., windowed thread).
Micro-optic devices such as the MOTION™ device may be designed such that when registered with the watermark(s), synthetic images projected thereby are combined with the watermark design(s). For example, in the above-referenced embodiment, the synthetic image(s) generated by each patch may coordinate or link in with the watermark design(s). The synthetic image(s) may also complete the watermark design(s) or locate within the design(s). As will be explained in more detail below, this may be a one-sided or two-sided feature.
In another such embodiment, the micro-optic security device(s), which is also described in, for example, U.S. Pat. No. 7,333,268, displays colored images (of any color, including white and black) on a translucent or substantially opaque background of a different color. In this embodiment, the micro-optic security device(s) at least partially covers and visually camouflages either the upper or face portion of the one or more watermarks, or the lower or back portion of the one or more watermarks. The watermark(s) is not visually discernible in reflected light from the covered side of the paper layer, but is visually evident in reflected light from the uncovered side of the paper layer, and in transmitted light from both sides of the paper layer.
An inherent benefit in the exemplary embodiments of the present invention which employ a partially or fully overlying or underlying film-like or foil-like security element such as the MOTION™ security device is the increased durability of each watermark. As is well known to those skilled in the art, one of the primary requirements of banknotes and other secure documents is that the document and its security features must resist the effects of circulation. These documents/features must be durable (i.e., resistant to fold damage, tearing and soiling) and resistant to moisture and chemical absorption. Covering all or part of the watermark(s) with an applied film, foil, band, strip, stripe, thread, or patch serves to physically protect the watermark(s) from damage during circulation and handling, thus increasing its durability.
Due to the increased durability afforded these watermarks, it has been determined that these watermarks may be made larger and that the total area within each watermark occupied by reduced fiber density regions (i.e., first regions) may be increased and that these regions may be made even thinner. Specifically, it has been found that these reduced fiber density regions may be produced with thicknesses as low as 10 to 15 microns, with total thicknesses ranging from about 10 to about 60 microns. The total area occupied by these reduced fiber density regions within each such watermark ranges from about 5 to about 75 percent (%) of the total area of the watermark, preferably from about 20 to about 60%. Moreover, the total area occupied by each such watermark within a banknote measuring approximately 10,000 square millimeters (mm2) may range from about 5 to about 25%, which denotes an increase in size compared to conventional watermarks of about 5%.
The present inventors have also made the surprising discovery that micro-optic devices such as the MOTION™ device may also offer a machine detectable/readable feature in the form of enhanced IR-brightness, especially when measured in transmission. The term “enhanced IR-brightness”, as used herein, is intended to mean IR-transmission levels of at least 5% greater than (preferably, more than 10% greater than) the IR-transmission levels of the background paper. IR-transmission levels may be measured by using an optical sensor with a sensitivity at or above 830 nanometers (nm) and by projecting an IR light source with a wavelength greater than 800 nm through the sample. To render IR-brightness a reliable machine readable feature, it is preferred that the micro-optic device be made using one or more IR-transparent elements (e.g., an IR-transparent ink) and contain no IR-absorbing elements (e.g., IR-absorbing inks). It is also preferred that no IR-absorbing elements be present in areas close to the device on the front and reverse side of the paper layer(s). In one such embodiment, the micro-optic device is a security thread (e.g., MOTION™ security thread) that contains no IR-absorbing elements. In this embodiment, the micro-optic security thread is made using an IR-transparent ink (e.g., ink comprising non-IR-absorbing pigments and/or dyes) for the microprint and areas on the front and reverse side of the paper layer(s) within at least two-thirds (⅔) of the security thread's length contain no IR-absorbing elements.
In addition to the at least partially overlying or underlying micro-optic device, one or more additional security features may be contained on or within the first and/or second regions of the one or more watermarks. In one such embodiment, the watermark(s) does not contain one or more polymer or resinous materials within the first and/or second regions. The additional security features are selected from the group of increased fiber density areas in the form of recognizable or discernible indicia, one or more substances that are color-imparting, and one or more second level security features that are machine detectable or machine readable, as described above.
In a second exemplary embodiment, the inventive security paper is a multi-ply paper that comprises:                a first paper layer having a reduced basis weight (e.g., from about 10 to about 50 grams per square meter (gsm)) and including one or more watermarks, each surface of the first paper layer displaying either the upper or face portion of the one or more watermarks or the lower or back portion thereof; and        a second paper layer having a reduced basis weight (e.g., from about 10 to about 50 gsm) and optionally one or more through windows, the second paper layer covering either the surface of the first paper layer displaying the upper or face portion of the one or more watermarks or the surface displaying the lower or back portion of the one or more watermarks.        
In one such embodiment, the second paper layer is windowed, the one or more through windows in the second paper layer being in register with either the upper or face portion or the lower or back portion of the one or more watermarks. By way of this second exemplary embodiment, the use of two paper layers and optionally one or more overlying or underlying through windows allows for a greater contrast between the one or more watermarks and the background. The one or more overlying or underlying through windows act in a manner similar to that of an electrotype, occupying paperless regions or regions of thinner paper which results in brighter-than-background regions in each paper/watermark region.
In a third exemplary embodiment, one or more security elements in the form of one or more color-imparting substances are contained within the first and/or second regions of the one or more watermarks. The one or more color-imparting substances include both dyes and pigments (e.g., ultra-fine particle size pigments). In this embodiment, the security sheet or document does not include one or more film-like or foil-like security elements. The resulting watermarks have a tonality (i.e., color scheme or range of tones) in a color or shade different from that of the bulk region of the material which surrounds the watermark. The inventive watermarks serve to increase the perception and resistance to simulation of existing watermarks.
In a fourth exemplary embodiment, one or more polymer or resinous materials are contained within the first region(s) and optionally the second region(s) of the one or more watermarks. As above, the security sheet or document in this exemplary embodiment does not include one or more film-like or foil-like security elements. The first and/or second regions in this embodiment may also contain one or more security features selected from the group of increased fiber density areas in the form of recognizable or discernible indicia, one or more substances that are color-imparting, and one or more second level security features that are machine detectable or machine readable, as described above.
In a fifth exemplary embodiment, the inventive security sheet or document is a single-ply paper that comprises:                a paper layer including one or more watermarks; and        one or more transparent or translucent areas in the paper layer surrounding each of the one or more watermarks, thereby framing and thus enhancing the visual perception of the watermark(s).        
Other features and advantages of the invention will be apparent to one of ordinary skill from the following detailed description and accompanying drawings.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods/processes, and examples are illustrative only and not intended to be limiting.